1. Field of the Invention
The present invention relates to an apparatus configured to perform color matching and a color matching method.
2. Description of the Related Art
FIG. 24 is a conceptual diagram of a common color matching. Input data, which is input device-independent data, for example, RGB data, is converted into data in XYZ values in a device-independent color space according to a profile of the input data. Since an output device cannot express colors which are not within a color gamut of the output device, a color gamut mapping is performed on the input data, which is converted into data of the device-independent color space so that any color is expressed in the color gamut of the output device. In the color gamut mapping, the data of the device-independent color space is converted into data of output device-dependent color space which is, for example, CMYK data.
The input device is, for example, a scanner, a digital camera, or a display. The output device is, for example, a printer.
FIG. 24 illustrates a color matching process performed by software called a color management system. Generally, ICC profiles defined by International Color Consortium (ICC) are used to describe color attributes of input and output devices. The ICC profiles include data indicating a relationship between a device-dependent color space and a device-independent color space (Profile Connection Space (PCS)) defined in a matrix or a look-up table (LUT). The widespread use of the ICC profiles has contributed to realization of easy color matching between the input and output devices.
Although the color matching using the ICC profile is highly convenient, undesirable results can appear in some cases. For example, while a monitor serving as an input device displays a color of pure yellow, a printer serving as an output device may produce a color that is not the pure color yellow but a mixture of different colors as a result of the color matching. The difference may be unnoticeable if the output data is a photo image. However, if the output data is text, which is generally expressed using a pure color, or vector data of graphics, the difference becomes noticeable.
Thus, in order to prevent output of an impure color with respect to an input of a primary color which is a color expressed by one color material such as yellow, cyan, or magenta, processing called “primary color compensation” is applied to the input data. In addition, processing called “secondary color secondary color compensation” is applied to an output of a secondary color which is expressed by mixing two primary colors, that is, red, green, and blue.
Japanese Patent Application Laid-Open No. 2002-171418 and U.S. Pat. No. 7,015,929 discuss compensation processing of the primary and the secondary colors. According to a technique discussed in Japanese Patent Application Laid-Open No. 2002-171418, if a color signal value of any input data is 0%, the input data is converted so that a corresponding color signal value of the output data becomes 0%. Further, according to a technique discussed in U.S. Pat. No. 7,015,929, pure color can be output also as to a color that is not within a specified input profile by using color space characteristics data including hue correction information of the printer which is stored in advance.
However, according to the technique discussed in Japanese Patent Application Laid-Open No. 2002-171418, the color signal value of the output data that corresponds to the input data is corrected to be 0% only when the color signal value of the input data is 0%. Consequently, discontinuity of colors may occur between the corrected data and uncorrected data in the vicinity of the corrected data.
According to the technique discussed in U.S. Pat. No. 7,015,929, continuity of colors is achieved between a primary color or a secondary color which is compensated, and a color in the vicinity of the compensated color even if the color is not included in a certain input profile. However, since certain fixed hue correction data is used for all input data, optimum hue correction processing cannot be applied to an arbitrary input profile. Further, color space characteristics data including hue correction information is necessary for each printer and extra memory area is required.
Thus, in order to dynamically switch between application and non-application of the primary color/secondary color compensation, either of the two techniques has to be chosen. One technique gives priority to memory efficiency at the sacrifice of color continuity as discussed in Japanese Patent Application Laid-Open No. 2002-171418. The other technique realizes natural color continuity but requires data (profile) for both cases of the primary color/secondary color compensation and non-color compensation as discussed in U.S. Pat. No. 7,015,929.